Foam laminate foil or web and process for preparing same

ABSTRACT

A foam laminate foil or web and process therefor. The laminate includes an unfoamed top layer containing an elastomer grafted styrene-acrylonitrile copolymer (ASA), grafted with polyfunctional acrylates and a chlorinated polyethylene (PEC) and/or a rubber-like ethylene-propylene mixed polymer (EPM) and/or a rubber-like terpolymer of ethylene, propylene and a diene, a closed pore polyolefin bottom layer with a bulk density of 30 kg/m 3  to 700 kg/m 3  which includes an ethylene homo- or copolymer, and an intermediate layer arranged between the bottom layer and the top layer and which acts as a coupling agent. The intermediate layer includes a low pressure polyethylene, an ethylene-vinyl ester copolymer and a rubber-like ethylene-propylene mixed polymer (EPM) and/or a rubber-like terpolymer of ethylene, propylene and a diene (EPDM).

BACKGROUND OF THE INVENTION

The present invention relates to a foam laminate foil or web, whichincludes a polyolefin foam foil or layer (top layer) (bottom layer), anonfoam top foil or nonfoam surface layer, containing a mixture or alloyof an elastomer grafted styrene-acrylonitrile copolymers (ASA) in acertain weight proportion, together with an intermediate foil or layerarranged between the polyolefin foam bottom layer and the top layer, theintermediate layer prepared from at least one low pressure polyethyleneand an ethylene vinyl ester copolymer or terpolymer.

In German Offenlegungsschrift No. 27 21 532 a process for thepreparation of composite foam foils is disclosed, wherein an unfoamedsynthetic plastic layer (B) consisting of a 20 μm-5mm thick layer, isapplied to a foamed synthetic plastic layer (A) consisting of a 1-120 mmthick foamed plastic web of an ethylene homo- or copolymer and having adensity between 10 g/l and 200 g/l. The layers are joined together bymeans of a compacting pressure, or else the layers (A) and (B) areadhesively joined by the use of a coupling agent coextruded with theunfoamed synthetic plastic layer (B). The synthetic materials for theunfoamed layer (B) are ethylene polymers. Other usable syntheticmaterials are styrene polymers, such as for example polystyrene,copolymers of styrene with the usual comonomers, such as acrylonitrile,acryl esters or maleic ester anhydride, which may be modified optionallyby rubbers based on butadiene or acryl ester polymers; also homo- orcopolymers of propylene, methylmethacrylate, vinyl chloride orvinylidene chloride. Thermoplastic polycondensates and polyadducts mayalso be used, such as for example polyamides, linear polyesters,polyacetates or polycarbonates.

Foam laminate foils, prepared by the process of GermanOffenlegungsschrift No. 27 21 532, comprise a polyethylene foam, anunfoamed layer or foil of a styrene-acrylonitrile copolymer and anintermediate layer of polyvinylacetate, but pose the risk ofdelamination at elevated temperatures, and thus the adhesion of theindividual layers to each other is inadequate for many applications.

Such delamination is particularly apparent in the 6-36 hour thermalaging test of molded parts at 120° C., by the separation of the top foilas the result of shrinkage phenomena from the polethylene foam. As thelayers of th coupling agents in most cases have lower physicalproperties than the surface foil and the PE foam, they affect theproperties of the composite detrimentally if used in the form of aheavier layer.

SUMMARY OF THE INVENTION

It is an object of the present invention to avoid the aforementioneddisadvantages by providing a foam laminate foil or web with improvedproperties.

It is another object of the invention to provide a foam laminate foil orweb which combines the specific properties of the styrene polymers,particularly their good hot formability, grain stability and agreeablefeel, with the typical properties of the polyolefins, without incurringthe danger of delamination or a deterioration of their deformationbehavior.

Still another object of the invention is to provide a process forpreparing the above-described foam laminate.

These objects are achieved by a delamination resistant foam laminate,comprising an unfoamed top layer having a thickness of greater thanabout 20 μm and comprising a styrene-acrylonitrile copolymer graftedwith at least one polyfunctional acrylate and containing at least oneadditional polymer selected from the group consisting of chlorinatedpolyethylenes, ethylene-propylene mixed polymers and a terpolymer ofethylene, propylene and a diene, the weight ratio of the graftedstyrene-acrylonitrile copolymer to the additional polymer or polymersbeing from about 8:2 to about 3:7; a polyolefin foam bottom layercomprising at least one polymer selected from the group consisting ofclosed pore polyethylene foams and closed pore ethylene-propylenecopolymer foams, the bulk density of the bottom layer being greater than10 kg/m³ ; and an intermediate layer arranged between the top and bottomlayers and acting as a coupling agent, the intermediate layer comprisinga mixture of a polar group-containing low pressure polyethylene, a polargroup-containing ethylene-vinyl ester copolymer and at least oneadditional polymer selected from the group consisting of rubber-likeethylene-propylene mixed polymers and rubber-like terpolymers ofethylene, propylene and a diene.

The objects of the invention are also achieved by a process forpreparing the above foam laminate, which includes the steps of joiningthe top, bottom and intermediate layers using joining means selectedfrom the group consisting of pressing, rolling, coextrusion andcombinations thereof. The laminate is heated during the joining step.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an embodiment of the laminate of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention relates to a foam laminate foil wherein the top foil orsurface layer composed of a mixture or alloy of an elastomer graftedstyrene-acrylonitrile copolymer (ASA) grafted with polyfunctional,preferably difunctional acrylates and a chlorinated polyethylene (PEC)and/or a rubber-like ethylene-propylene mixed polymer (EPM) and/or arubber-like terpolymer of ethylene, propylene and a diene, preferably anonconjugated diene (EPDM), wherein the weight proportions (ASA) to(PEC) and/or (EPM) and/or (EPDM) amount to 8:2 to 3:7, preferably 6:4 to4:6. The polyolefin foam foil or layer (bottom foil) comprises a closedpore polyethylene foam and/or a closed pore ethylene-propylene copolymerfoam or mixtures of these synthetic materials, with a bulk density of 30to 700 kg/m³, preferably 35 to 500 kg/m³. The intermediate foil orintermediate layer comprises a mixture or alloy of a mixture or alloycontaining polar groups of a low pressure polyethylene containing polargroups and an ethylene-vinyl ester copolymer containing polar groups,preferably an ethylene-vinyl acetate modified low pressure polyethylene(HDPE), and a rubber-like ethylene-propylene mixed polymer (EPM) and/ora rubber like terpolymer of ethylene, propylene and a diene (EPDM).

FIG. 1 illustrates an example of an embodiment of the invention in aschematic view. The top foil (11) is joined by means of the intermediatelayer (12) to the polyolefin foam foil or layer (10) (representing thebottom layer or foil).

The foam laminate foil or web according to the invention has good hotformability, a slight change in embossed patterns due to heating toforming temperatures, low hardening of the laminate during deformation,good aging behavior, no delamination during processing and applicationand further processing advantages and improved properties of theproduct.

The intermediate foil is adapted according to the invention in its hotforming stability, its mechancial properties and deep drawing behaviorto the top foil. In this manner, the typical properties of the styrenepolymers may be combined with those of the polyolefins. As specificproperties of styrene polymers, good hot formability, grain stabilityand agreeable feel are mentioned. The modified polyolefins in particularimprove low temperature properties.

As the mechanical properties of the intermediate foil are adapted tothose of the surface foil, their thickness proportions may be variedwithin a wide range. However, the thickness ratio between the top foilor surface layer and the intermediate layer appropriately amounts to 4:1to 1:4, preferably 3:1 to 1:3.

According to a preferred embodiment, the weight proportion in the topfoil or surface layer of chlorinated polyethylene (PEC) to therubber-like terpolymer of ethylene, propylene and a diene (EPDM) and/orto the rubber-like ethylene-propylene mixed polymer (EPM) amounts to 1:3to 3:1, preferably 1:2 to 2:1. In the intermediate layer, the vinylester content (with respect to the entire mixture or alloy of syntheticsubstances of the intermediate layer), preferably the vinyl acetatecontent (or vinyl acetate unit content) amounts to 5-20 parts by weight,preferably 6-18 parts by weight (with respect to 100 parts by weight ofthe mixture or alloy of synthetic substances and calculated withoutauxiliary processing means, fillers or additives). With the use of thiscomposition it is possible, among other things, to reduce or eliminatethe risk of delamination.

According to a preferred embodiment, the EPM and/or EPDM content in theintermediate layer is from about 6 to about 27 parts by weight,preferably 7-24 parts by weight, (with respect to 100 parts by weight ofthe synthetic material mixture or alloy of the intermediate layer andcalculated without processing aids, fillers or additives). With thiscomposition of the foam laminate foils an especially low hardening ofthe laminate after deformation, and a reduction of the danger ofdelamination and the like, are obtained. The ethylene-vinyl estercopolymers containing polar groups and used for the intermediate layerare preferably ethylene-vinyl acetate copolymers, and have a vinylester, preferably a vinyl acetate content (vinyl acetate unit content)of 9-40% by weight, preferably 12-30% by weight.

The chlorinated polyethylene (PEC) contained according to one embodimentin the top foil or surface layer preferably has a chlorine content of36-46% by weight. The top foil or surface layer contains according to afurther embodiment, 0.5-5% by weight, preferably 2-4% by weight (withrespect to 100% by weight of the synthetic substance mixture of the topfoil) of a polycaprolactone. The closed pore polyethylene foam and/orclosed pore ethylene-propylene copolymer foam or closed pore foam ofmixtures of these synthetic substances is not crosslinked and has a bulkdensity of 300-700 kg/m³, preferably 320-500 kg/m³.

According to a still further embodiment, the closed pore polyethylenefoam is cross-linked by a physical and/or chemical process known per seand/or the closed pore ethylene-propylene copolymer foam is cross-linkedand has a bulk density of 30-300 kg/m³, preferably 35-280 kg/m³. Theintermediate foil or intermediate layer and the top foil or surfacelayer have a total thickness of 0.1-1.5 mm, preferably 0.3-0.8 mm. Thepolar group-containing ethylene-vinyl acetate copolymer has a meltingindex Mfi 190/2.16 of 1-10 g/10 min.

The invention further concerns a process for the preparation of theabove described foam laminate foils or webs. The layers are joined orbonded together, without the use of additional adhesives, by pressing inknown pressing or rolling installations and/or by the use of acoextrusion process with the application of heat.

The surface layer exiting from a sheet die and the intermediate layerare combined without the use of additional adhesives at a masstemperature of 180° C. to 260° C., preferably 200° C. to 240° C., withthe poyolefin foam foil or web at a line pressure of 2 to 50 kp/cm, withthe use of at least one pair of rolls, preferably using an embossingroll or a press.

According to a further embodiment, the top foils and/or bottom foilsand/or intermediate foils are prepared separately and/or in the form oftwo-layer foils and joined by means of a press or at least one pair ofrolls, with the other foils or the third foil at an intermediatetemperature of 130°-250° C., preferably 140°-190° C., by pressingwithout the use of additional adhesives.

According to another preferred embodiment, the top layer, bottom layerand intermediate layer are joined by coextrusion at a mass temperatureof 180°-260° C., preferably 200°-240° C. and produced by means of asheet die.

The foam laminate foils or webs according to the invention may beapplied directly as such or they may be exposed to further working orprocessing, for example, hot deformation, deep drawing or embossingand/or secondary foaming, or the like.

The foils according to the invention are adapted in regard to theirthermoforming stability, their mechanical properties and deep drawingbehavior, to the top foil. In this manner, the typical properties ofstyrene may be combined advantageously with those of polyolefins. Asparticular properties of styrene polymers, good thermoformabilty, grainstability and agreeable feel may be mentioned. Modified polyolefinsimprove in particular low temperature properties.

COMPARATIVE EXAMPLE 1

The 300 μ m thick top foil consisted, in this comparative example whichis not part of the prior art, or a mixture of

65 parts of weight of an acrylate grafted styrene-acrylonitrilecopolymer (ASA)--acrylate proportion approx. 40% by weight,

25 parts by weight PEC--chlorine content 42%

10 parts by weight EPDM--ethylene content 70%,

and was prepared by calendering at 180° C.

The intermediate layer consisted of HDPE Mfi 190/2.16 of 1 g/10 min, anehtylene-vinyl acetate (EVA) copolymer with a proportion of 28% VAc anda Mfi 190/2.16 of 3 g/10 min, in mixing proportions according to thetable below. The mixtures were extruded at 180° C. to 200 μ m thickfoils.

The bottom layer consisted of a cross-linked HDPE foam with bulk densityof 35 kg/m³.

The 3 layers were pressed in a press at 170° C. for 2 min with apressure of 5 kg/cm².

The values listed in Table I were determined by the appropriate DIN(German Industrial Standard) testing methods.

                  TABLE I                                                         ______________________________________                                                   Mixing prop. HDPE/EVA                                              Phys. prop.  9:1    8:2      7:3  6:4    4:6                                  ______________________________________                                        Utl. tensile strength                                                                      21.5    17      15.5 15     13                                   longitudinal, (N/mm.sup.2)                                                    Utl. tensile strength                                                                       21     16       15  15     14                                   transverse (N/mm.sup.2)                                                       Elongation   170    130      125  205    440                                  longitudinal (%)                                                              Elongation   260    105      140  185    360                                  transverse (%)                                                                Shore D hardness                                                                            64     60       57  55     53                                   VSP (A)      132    115      112  89     77                                   °C.                                                                    Adhesion     5.9    12.5      27  30     30 min                               (N/5 cm)                          min    unsep-                                                                        arable                               VAc content  2.8    5.6       8.4 12.2   16.8                                 (% by weight)                                                                 ______________________________________                                    

The tensile tests showed a limited compatibility of the two polymers, asthe ultimate tensile strength declined with increasing proportions ofEVA and the elongation was not improved. The vacuum deformation of thelaminate was not adequate, as at temperatures above 120° C. theintermediate layer ruptured without a satisfactory deformation of thetop foil. Adhesion in these combinations was adequate only beginningwith a VAc proportion of 12% by weight.

EXAMPLE 1

In the intermediate layer according to Comparative Example 1, the HDPEwas replaced in part by EPDM according to the invention, while otherwisefollowing the process of Comparative Example 1. Results are compiled inTable II.

                                      TABLE II                                    __________________________________________________________________________               Mixing prop. HDPE/EPDM Eva                                         Physical prop.                                                                           6.3:2.7:1                                                                          5.6:2.4:2                                                                          4.9:2.1:3                                                                           4.2:1.8:4                                                                           2.8:1.2:6                                    __________________________________________________________________________    Utl. tensile strength                                                                    19.5 19.2 18.5  18    18.3                                         longitudinal, (N/mm.sup.2)                                                    Utl. tensile strength                                                                    19.2 19   18    17.8  18                                           transverse (N/mm.sup.2)                                                       Elongation 870  860  830   845   855                                          (%)                                                                           Elongation 820  865  840   820   830                                          transverse (%)                                                                Shore D hardness                                                                          52  50   47    43    40                                           VSP (A)    110  95   82    77    73                                           °C.                                                                    Adhesion    7.5 3.8  unseparable                                                                         unseparable                                                                         unseparable                                  (N/5 cm)                                                                      VAC content                                                                               2.8 5.6  8.4   12.2  26.8                                         (% by weight)                                                                 __________________________________________________________________________

The results of tensile testing showed that the test results wereindependent of the mixing proportion and that therefore "practical"compatibility was present. Furthermore, the adhesion properties requiredwere obtained already with a VAC content of 8.4%. Deep drawing testsindicated that deformations could be effected within a range of 120° to160° C. and that satisfactory contours are thereby obtained.

The foregoing description of preferred embodiments has been set forthmerely to illustrate the invention and is not intended to be limiting.Since modifications of the described embodiments incorporating thespirit and substance of the invention may occur to persons skilled inthe art, the scope of the invention should be limited solely withrespect to the appended claims and equivalents.

What is claimed is:
 1. A delamination resistant foam laminate,comprising:an unfoamed top layer having a thickness of greater thanabout 20 μ m and comprising a styrene-acrylonitrile copolymer graftedwith at least one polyfunctional acrylate and containing at least oneadditional polymer selected from the group consisting of chlorinatedpolyethylenes, ethylene-propylene mixed polymers and a terpolymer ofethylene, propylene and a diene, the weight ratio of said graftedstyrene-acrylonitrile copolymer to said at least one additional polymerbeing from about 8:2 to about 3:7; a polyolefin foam bottom layercomprising at least one polymer selected from the group consisting ofclosed pore polyethylene foams and closed pore ethylene-propylenecopolymer foams, the bulk density of said bottom layer being greaterthan 10 kg/m³ ; and an intermediate layer arranged between said top andbottom layers and acting as a coupling agent, said intermediate layercomprising a mixture of a polar group-containing low pressurepolyethylene, a polar group-containing ethylene-vinly ester copolymerand at least one additional polymer selected from the group consistingof rubber-like ethylene-propylene mixed polymers and rubber-liketerpolymers of ethylene, propylene and a diene.
 2. A foam laminateaccording to claim 1, wherein said styrene-acrylonitrile copolymer ofsaid top layer is grafted with a difunctional acrylate, and wherein saiddiene in said top layer is nonconjugated.
 3. A foam laminate accordingto claim 1, wherein the weight ratio of said graftedstyrene-acrylonitrile copolymer to said at least one additional polymerin said top layer is from about 6:4 to about 4:6.
 4. A foam laminateaccording to claim 1 wherein the bulk density of said bottom layer isfrom about 30 to about 700 kg/m³.
 5. A foam laminate according to claim1 wherein the bulk density of said bottom layer is from about 35 toabout 500 kg/m³.
 6. A foam laminate according to claim 1 wherein saidethylene-vinyl ester copolymer of said intermediate layer isethylene-vinyl acetate.
 7. A foam laminate according to claim 6 whereinsaid ethylene-vinyl acetate copolymer has a melt flow index 190/2.16 offrom about 1 to about 10 g/min.
 8. A foam laminate according to claim 1,wherein the ratio thicknesses between said top layer and saidintermediate layer is from about 4:1 to about 1:4.
 9. A foam laminateaccording to claim 1, wherein the ratio thicknesses between said toplayer and said intermediate layer is from about 3:1 to about 1:3.
 10. Afoam laminate according to claim 1 wherein said top layer contains atleast two said additional polymers, one of said additional polymersbeing a chlorinated polyethylene, and wherein the ratio of saidchlorinated polyethylene to the other said additional polymers is fromabout 1:3 to about 3:1.
 11. A foam laminate according to claim 1 whereinsaid top layer contains at least two said additional polymers, one ofsaid additional polymers being a chlorinated polyethylene, and whereinthe ratio of said chlorinated polyethylene to the other said additionalpolymers is from about 1:2 to about 2:1.
 12. A foam laminate accordingto claim 1 wherein the vinyl ester content in said ethylene-vinyl esterof said intermediate layer comprises from about 5 to about 20 parts byweight per 100 parts by weight of total polymer in said intermediatelayer.
 13. A foam laminate according to claim 1 wherein the vinyl estercontent in said ethylene-vinyl ester of said intermediate layercomprises from about 6 to about 18 parts by weight per 100 parts byweight of total polymer in said intermediate layer.
 14. A foam laminateaccording to claim 1 wherein said at least one additional polymer insaid intermediate layer comprises from about 6 to about 27 parts byweight per 100 parts by weight of total polymer in said intermediatelayer.
 15. A foam laminate according to claim 1 wherein said at leastone additional polymer in said intermediate layer comprises from about 7to about 24 parts by weight per 100 parts by weight of total polymer insaid intermediate layer.
 16. A foam laminate according to claim 1wherein the vinyl ester content of said ethylene-vinyl ester is saidintermediate layer is from about 9% to about 40% by weight.
 17. A foamlaminate according to claim 1 wherein the vinyl ester in saidintermediate layer content of said ethylene-vinyl ester is from about12% to about 30% by weight.
 18. A foam laminate according to claim 1wherein said top layer contains one or more chlorinated polyethyleneshaving a chlorine content of from about 36% to about 46% by weight. 19.A foam laminate according to claim 1 wherein said top layer containspolycaprolactone in an amount of from about 0.5% to about 5% by weightbased on the total polymer weight in said top layer.
 20. A foam laminateaccording to claim 1 wherein said top layer contains polycaprolactone inan amount of from about 0.2% to about 4% by weight based on the totalpolymer weight in said top layer.
 21. A foam laminate according to claim1 wherein said at least one polymer in said bottom layer isuncrosslinked and has a bulk density of from about 300 to about 700kg/m³.
 22. A foam laminate according to claim 1 wherein said at leastone polymer in said bottom layer is uncrosslinked and has a bulk densityof from about 320 to about 500 kg/m³.
 23. A foam laminate according toclaim 1 wherein said at least one polymer in said bottom layer iscrosslinked and has a bulk density of from about 30 to about 300 kg/m³.24. A foam laminate according to claim 1 wherein said at least onepolymer in said bottom layer is crosslinked and has a bulk density offrom about 35 to about 280 kg/m³.
 25. A process for preparing adelamination resistant foam laminate, comprising:joining a top layer, abottom layer and an intermediate layer without the use of additionaladhesives using joining means selected from the group consisting ofpressing, rolling, coextrusion and combinations thereof; and heating thelaminate during said joining step; wherein said top layer comprises anunfoamed layer having a thickness of greater than about 20 μm andcomprising a styrene-acrylonitrile copolymer grafted with at least onepolyfunctional acrylate and containing at least one additional polymerselected from the group consisting of chlorinated polyethylenes,ethylene-propylene mixed polymers and a terpolymer of ethylene,propylene and a diene, the weight ratio of said graftedstyrene-acrylonitrile copolymer to said at least one additional polymerbeing from about 8:2 to about 3:7; wherein said bottom layer comprises apolyolefin which includes at least one polymer selected from the groupconsisting of closed pore polyethylene foams and closed poreethylene-propylene copolymer foams, the bulk density of said bottomlayer being greater than 10 kg/m³ ; and wherein said intermediate layercomprises a mixture of a polar group-containing low pressurepolyethylene, a polar group-containing ethylene-vinyl ester copolymerand at least one additional polymer selected from the group consistingof rubber-like ethylene-propylene mixed polymers and rubber-liketerpolymers of ethylene, propylene and a diene.
 26. A process accordingto claim 25, wherein said process includes the step of extruding saidtop layer through a sheet die and wherein said joining step is performedat a temperature of from about 180° C. to about 260° C.
 27. A processaccording to claim 26, wherein said intermediate layer is joined withone of said top and said bottom layers separately to form a two-layerlaminate, and two-layer laminate thereafter joined to the other of saidtop and bottom layers at a temperature of from about 130° C. to about250° C. and by joining means selected from pressing and at least onepair of rolls.
 28. A process according to claim 27, wherein saidtwo-layer laminate is joined to said other layer at a temperature offrom about 140° C. to about 190° C. by means of pressing.
 29. A processaccording to claim 25, wherein said joining means comprises coextrusionof said top, bottom and intermediate layers at a temperature of fromabout 180° C. to about 260° C., said coextrusion utilizing a sheet die.30. A process according to claim 29, wherin said coextrusion temperatureis from about 200° C. to about 240° C.